Or three stages. Then you can make the first stage out of a low cost
Mach 0.8 plane

To my mind, it doesn't really count as a stage unless it contributes
significant delta-V -- the aircraft is a launch platform. Nevertheless,
that can be a useful approach if you can live within its limitations.

Quote:

A Mach 0.8 aircraft can be off the shelf. Or even better, if you
beleive scaled composites, composite technology allows the building of
low cost custom large aircraft, as proposed for T-space.

Maybe. Rutan has an excellent record of building impressive prototypes.
His record of carrying them through to certification for operational
service isn't so good (although admittedly a lot of the problem is the
certification process and its administrators). And his costs don't look
quite so low, or his schedules quite so short, if your goalpost is
certification rather than first flight. There's something to be said
for off the shelf, even if the aircraft isn't ideal.

Quote:

This doesn't help much with delta V, but improves launch location
(altitude and position)...

Which does help indirectly with delta V, by improving engine Isp (thinner
air) and possibly by permitting a quicker mission with less post-launch
maneuvering (if the job involves rendezvous).
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net

Your post is data-rich, and Henrys opinion is respected.
I'm preaching to the choir but I figure our bench-marks
are the Saturn V and/or the Shuttle.
It's obviously cost-effective to use an engine that costs
10x more if you can use it 50 times...ok, that was the
rationale of the Shuttle over the SatV, and it worked.

Actually, it didn't work all that well, especially at the beginning. The
problem with the SSME's wasn't necessarily that they were expensive to
build, but they were expensive to maintain. At the beginning of the
program, NASA would pull the engines from a flown shuttle and tear them all
down for a rebuild/inspection. Things have gotten quite a bit better over
the years, but that was due to continuous development and improvement on
things like the turbopumps.

The lesson to learn from the SSME isn't that reusing a rocket engine is
hard, it's that high compression, high ISP engines that run from sea level
to vaccuum aren't such a good idea unless you can actually reuse them
without tearing them apart after every flight.

Quote:

An air breathing re-usable Mach 10+ ramjet for a 2nd
stage is reasonable quest, the 1st gets her up to
Mach 1 using cheapo SRB's, and the 3rd does
orbital insertion, and if you want that can be re-entered
and reused, that's all proven.
I suggest we Build & Blast until we get it right,
then we own cheap LEO, that's the goal!
Regards
Ken S. Tucker
PS: Is the ISP of a ramjet >2000

Again, who cares. How much money do you have to spend to get that ISP?
What matters is the cost to reliably put mass into LEO measured as $/lb. As
such, I don't believe that the first stage you're describing would be good
from a $/lb perspective.

A reusable, kerosene/LOX rocket powered, VTVL first stage built with
conventional materials would be a better way to go for a reusable first
stage. Your approach is trying to minimize the LOX and kerosene burned
(high ISP) and that's silly when LOX is one of the cheapest fluids on the
planet and kerosene is still an extremely small part of overall launch
costs.

I was originally thinking it could telescope in, but like I indicated,
that might be difficult.

For awhile I was really looking for an engine with a variable bypass
ratio.

Quote:

The blades are quite a bit longer than the hub diameter,
and it's not like there's a lot of unused space inside a jet engine.

It would be nice to have the assembly counter rotate down to the ocean
like a maple tree seed. Fans are already made of carbon.

Depends on whose engine you're looking at. Most fan's aren't carbon.

That will certainly change if titanium stays above $35/lb.

Quote:

And a well-optimized turbofan core doesn't resemble a Mach 2 turbojet
all that closely.

Instead of expanding in the last turbine the gas is reheated in the
after burner.

You can't seriously be discussing propulsion efficiency and then throw an
afterburner into the equation. Afterburner is just a way of augmenting
thrust with a *ferocious* efficiency penalty...you do it because you have
to, not because you want to. A supercruise engine would do far better from
an efficiency standpoint.

It wouldn't be in afterburner mode all the way across the Pacific
Ocean. The idea was to try to get an airbreather to _accellerate_ up
to scram speeds.

Quote:

High speed propulsion is going to require some sophistication no matter
what you try.

Highest speed propulsion = rocket = lowest sophistication.

A missile with a cheap solid rocket motor can outrun the best jets ever
built.

In article <1150983258.730309.257020@y41g2000cwy.googlegroups.com>,
Alex Terrell <alexterrell@yahoo.com> wrote:
Or three stages. Then you can make the first stage out of a low cost
Mach 0.8 plane

To my mind, it doesn't really count as a stage unless it contributes
significant delta-V -- the aircraft is a launch platform. Nevertheless,
that can be a useful approach if you can live within its limitations.

A Mach 0.8 aircraft can be off the shelf. Or even better, if you
beleive scaled composites, composite technology allows the building of
low cost custom large aircraft, as proposed for T-space.

Maybe. Rutan has an excellent record of building impressive prototypes.
His record of carrying them through to certification for operational
service isn't so good (although admittedly a lot of the problem is the
certification process and its administrators). And his costs don't look
quite so low, or his schedules quite so short, if your goalpost is
certification rather than first flight. There's something to be said
for off the shelf, even if the aircraft isn't ideal.

This doesn't help much with delta V, but improves launch location
(altitude and position)...

Which does help indirectly with delta V, by improving engine Isp (thinner
air) and possibly by permitting a quicker mission with less post-launch
maneuvering (if the job involves rendezvous).
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net

Which does help indirectly with delta V, by improving engine Isp (thinner
air) and possibly by permitting a quicker mission with less post-launch
maneuvering (if the job involves rendezvous).
--
A not so obvious cost and benefit is that it forces a streamlining of

launch operations. Launch control has to be simpler and leaner. (Though
SpaceX have already done this by forcing everything into one trailer).

T-Space have also designed a drop launch mechanism (rather than launch
off the plane), which allows a very safe abort. If the engine fails,
the crew or cargo have 10,000 metres of falling to get the parachute
outs (or say good bye if the parachute doesn't work).

The lesson to learn from the SSME isn't that reusing a rocket engine is
hard, it's that high compression, high ISP engines that run from sea level
to vaccuum aren't such a good idea unless you can actually reuse them
without tearing them apart after every flight.

As you say, the SSMEs have gotten better. They are no longer torn
apart after each flight.

The more basic lesson to learn is that it's stupid to develop new vehicles
(with new engines) that will end up only being used 130 times or so.

The lesson to learn from the SSME isn't that reusing a rocket engine
is hard, it's that high compression, high ISP engines that run from
sea level to vaccuum aren't such a good idea unless you can actually
reuse them without tearing them apart after every flight.

As you say, the SSMEs have gotten better. They are no longer torn
apart after each flight.

I would expect that next generation high Isp, high thrust engines
(perhaps of the full flow variety, or the run of the mill Cobra or
whatever variety) will be even better. The trick, of course, is to get
them back to the launch site in fairly good shape in very little time.

Quote:

The more basic lesson to learn is that it's stupid to develop new vehicles
(with new engines) that will end up only being used 130 times or so.

Let's see, at 2 flights a year, how long will it take to make 130 Apollo
II flights?

Quote:

Now, why are we developing a heavy lift vehicle?

Good question. Unless we reuse the engines, and deliver the cryogenic
tankage to orbit, there is no reason whatsoever. On the other hand, a
relatively inexpensive HLV solution, with a high flight rate (12/year or
once a month), and that returns the engines intact in short order, and
delivers a preengineered fully flight functional cryogenic tank to
orbit, would, by any metric, be a major space technology breakthrough.

We are that close, folks. With or without the SRBs, a ten meter ET that
can be manufactured at a rate of 12 per year, and reusable SSMEs (or
their second generation equivalent), are the answer to our problems.

If we have to use the Space Shuttle, ISS, RS-68 and the Delta IV Medium
in order to work out the details, then fine, but my money is on that 10
meter ET and the SSMEs, in an unmanned heavy lift launch configuration,
that returns the engines to the vicinity of the launch site within two
hours and delivers fully functional cryogenic spacecraft to LEO and GEO.

Who cares? What we're trying to optimize is cost, not dry mass of the
launch vehicle or any sort of efficiency you can measure on the launch
vehicle.

As Henry said, fuel and oxidizer are cheap, at least they are if you pick
reasonable propellants. A favorite of mine is LOX/kerosene. LOX is one of
....
Also, tankage is cheap and the thrust to weight ratio of a rocket engine is
better than that of an airbreather built to operate over a wide range of
speeds (subsonic to several Mach numbers). That and a rocket engine isn't
as complex as such an airbreather. Plus you have the fact that there simply
aren't that many air breathing engines to choose from if you expect them to
operate over a wide range of speeds. Most air breathing engines are
optimized for subsonic cruise, with a few optimized for supersonic cruise
(e.g. SR-71, Concorde, and some modern jet fighters).

So exactly why would anyone prefer a costly, complex, heavy air breathing
engine for rapid acceleration of a launch vehicle, when you can use a more
simple, lighter, cheaper, LOX/kerosene first stage engine instead?

I proposed some time ago in sci.space.tech a solution for a "zeroth"
stage that would boost the rocket up maybe 150 m/s or so and radically
lessen gravity losses.
The usefulness of a zeroth stage is discussed here:
http://ambivalentengineer.blogspot.com/2006/05/three-stage-to-orbit.html
A 300 m/s boost would allow stretching the tanks (same engines) and
delivering about thrice the two-stage payload to orbit. A small boost
might not seem much, but if the rocket has a thrust to weight initially
close to 1, it doesn't accelerate much but it travels up at that
300 m/s still and that lessens gravity losses a lot.

My zeroth stage would consist of helicopter rotors getting their
power from the rocket turbopump. The fuel consumption would only
be a few percent of the full-throttle operation (that much is diverted
typically to the gas generator), and not much additional hardware
would be needed. Just a gearbox and a clutch. It's been hard
to get gas generator power levels, but some, when compared to
helicopters seem to be just about having enough power to lift the
rocket, at least at low speed.

The idea is that using the stationary air as reaction mass
is extremely effective at low speeds. It's more of a hindrance
at mach 1 and above but the stage can be discarded long before and
the rocket can operate conventionally. The rotor assembly is easy
to be made to descend at very low speed and be recovered for
reuse.

Note that this is NOT a tip-rocket rotor like Roton or Hiller.
There are no difficult fuel columns inside the fast spinning
rotor(s). Just somewhat ordinary helicopter rotors. I guess they'd
have to be special to operate at such wide speed regime along the
rotation axis (but they gimbal anyway), and I don't know what
efficiency can be gained, I'm totally clueless about the
aerodynamics here. You'd have to have lots of blades to limit
tip speed at least.

Turbopumps and combustion chambers ain't cheap, even if tanks
were, and with this system one can keep them at existing
size and still boost the performance tens of percents, maybe
close to 100%. It might still not be commercially viable,
but it would be cool to talk about the idea's technical
feasibility.

My zeroth stage would consist of helicopter rotors getting their
power from the rocket turbopump. The fuel consumption would only
be a few percent of the full-throttle operation (that much is diverted
typically to the gas generator), and not much additional hardware
would be needed. Just a gearbox and a clutch.

"Just a gearbox and a clutch" is a *huge* technical hurdle.

The gearbox of a helicopter is the heart of the whole thing, along with the
rotor. You're talking about a really big rotor to get the lift for a really
good rocket payload (plus all the fuel), which means really slow rotation.
So your gearbox has to get turbopump speed (extremely high) down to slow
rotor speed, carrying more more power than any helicopter gearbox ever made,
and do it at a low-enough cost, highe-enough efficiency, and low-enough
weight to economically override just adding another rocket stage.

I'm not saying it's impossible, but as technical achievements go it would
rank right up there with the all-time toughies.

Maybe use the old McDonnel-Douglas engine tipped rotor idea. They used
small rams in their test rig but maybe something else would be better.
Is the tip speed sonic or close to half the exhaust velocity?

With a stator blade ring you could recover some of the kinetic energy
lost in the exhaust.

.. . .

Quote:

You're talking about a really big rotor

Hard to spin balance, hard to test, hard to haul down the interstate
but maybe you could reassemble it on site.

People are as bored with that smokey thing as they are with 9/11 video.
It was good for awhile . . .